UNIT-5

Cables, Connectors

and

Measuring Instruments

Index

5.1 Analog and Digital display.

5.2 Cables: coaxial cable, twisted pair cable and fiber optic

cable

5.3 Connectors: coaxial cable connectors, RJ-45, RS-232,

HDMI connectors

5.4 Multimeters: Analog and digital multimeter

5.5 CRO: front panel controls and application

Different electrical quantity and instrument for

measuring them:Voltage:

• By using voltmeter, we can measure voltage and

potential difference.

• There are Two types: A.C. and D.C.

• It is available in wide range and it always

connected in parallel.

Current:

• By using ammeter, we can measure current.

• There are two types: A.C. and D.C.

• It always connected in parallel and available in wide

range

Power:

• By using wattmeter, we can measure power. There are

two coils. one is current coil which is connected in

series. second is pressure coil which is connected in

parallel like voltmeter.

Energy:

Frequency :

Power factor :

• Electrical energy is measured by energy meter.

• Frequency of A.C. supply is measured by

frequency meter.

• power factor of load is measured by power factor meter.

5.1 Analog and digital display(LED and LCD):

Analog display

• In analog type , there are two main parts. one

part is moving and other part is stationary.

• The part which move is called moving part.

• It is mounted on spindle.

• The spindle is pivoted on the jewel bearings.

• A pointer is attached to the spindle which moves

over the graduated scale.

Digital display

• There is no moving part. The quantity measured is

converted into analog to digital and it is display on the

panel.

• Types of digital display

(1) LED Display

(2) LCD Display

LED display

• Light Emitting Diode

• It is one type of junction diode. It emits light when it is

forward biased.

• The color of light depends upon the material of the diode.

• Seven segment are arranged and by exciting the particular

segment , several numerals can be displayed.

LCD display

• In LCD type display, liquid crystals are used.

• These crystals are kept between two transparent glass plate.

When electric field is not applied.

• Crystal look transparent as these are arranged in definite

pattern .But when certain part is excited the crystal in that

part are disturbed so that portion looks black.

5.2 Cables:

Cables are used to carry electrical signal.

General specification of cable:

1) characteristic impedance

2) current carrying capacity

3) size of cable

4) flexibility

Types of cable:

1) ribbon cable

2) screen cable

3) co-axial cable

4) twisted pair cable

5) fibre optic cable

Co-axial cable:

• There is one core of Stranded

copper conductor or single core

of copper conductor. Over the

core the insulation made of PVC

is provided. Surrounding the

insulation a metal screen is

provided.

• In production of co-axial cable , precise control of the

insulation and its thickness is done so that the characteristic

impedance of 50Ω, 75Ω or 95Ω or required impedance is

achieved.

Types of co-axial cable:

1. RG-8 and RG-11(thicknet)

2. RG-58(thinnet)

RG-8 and RG-11(thicknet)

1. Its thickness is 12 mm.

2. It is used for the distance of 500m.

3. Its name thicknet indicates that its thickness is more.

4. noise immunity is good.

5. Its cost is more due to the increased thickness.

6. Due to increased thickness its flexibility is more.

RG-58(thinnet)

1. The thickness of this type of cable is 6mm.

2. It is used for the distance of 185m.

3. Due to its small thickness, flexibility is good and

cost is less

4. There are two types:RG-59 ,RG-62.

Application

• It is used in cables for TV camera

• It is used in multiplexed data tele -data acquisition

system

• It is used in mines for communication

• It is employed in CCTV system.

• Low noise RF cables are used for the space craft

signal.

Ribbon cable:

Screened cable

Twisted pair cable:

• Twisted-pair is a type of cabling that is used for

telephone communications

• A pair of wires forms a circuit that can transmit data.

• The pairs are twisted to provide protection against

crosstalk, the noise generated by adjacent pairs.

• There are two basic types, shielded twisted-pair (STP) and

unshielded twisted-pair (UTP).

• Consists of 4 pairs (8 wires) of insulated copper wires

typically about 1 mm thick.

• The wires are twisted together in a helical form.

• Twisting reduces the interference between pairs of wires.

• High bandwidth and High attenuation channel.

• Flexible and cheap cable.

• Category rating based on number of twists per inch and

the material used

• CAT 3, CAT 4, CAT 5, Enhanced CAT 5 and now CAT 6.

• UTP comes in several categories that are based on the

number of twists in the wires, the diameter of the wires and

the material used in the wires.

• In this type of cable, there are many pairs of twisted

conductors. Insulations of different color are provided over

the core.

• Each pair is twisted.

• In STP, a metal screen or metal foil is wrapped round each

twisted pair. Number of twisted pair are four. Overall

screen is provided over the four pairs.

Fiber optic cable:

• In this, fiber is used in place of conductor and light ray

is used instead of electric current.

Principle of optical fiber

• When the ray of light travels from the dense medium to the

light medium and if angle of incident is equal to the

critical angle, there is total reflection of the ray. so the ray

does not go to the light medium.

• The refractive index of central core is n2 and that of outer

wall is n1 and n2>n1.So the incident ray does not go out of

the fiber and come out after repeated reflection.

Single-mode fiberCarries light pulses along single pathUses Laser Light Source

Multimode fiberMany pulses of light generated by LED travel at different angles

Types of fiber optic cable:

• plastic core and cladding

• glass core and plastic cladding

• glass core and cladding

• high band width

• less attenuation

• light in weight

• best security

• no effects of noise

Advantages:

Application of fiber optic cable:

• Short wave and long wave

transmission telecommunication

• Digital transmission

• Highway traffic control

• Office automation system

• High resolution TV system

• Submarine optical fiber system

Connector:

It is used to connect two device or two electronics

equipment.

5.3 Connectors: coaxial cable connectors, RJ-45,

RS-232, HDMI connectors

• There are different types of connectors.

• Here ,we study about RF connector which are

used with co-axial cable and tele –communication

connector.

RF connector:

• BNC(Bayonet Neil Connector)

• TNC(Threaded Neil Concelman Connectors)

• N

• UHF

• RF connector are design for radio frequency voltage and

current.

• These are made in different range and characteristic.

1) BNC : Bayonet Neil Connector

• As the locking system, it can be connected or

disconnected easily. Shell is made from brass and it is

nickel plated. Middle contact is made of brass and it is

gold or silver plated. Teflon is used as dielectric.

• The size of this connector is small.

• Its weight is light and Its nominal

impedance is 50Ω.

• It is used in CRO, TV, radar , digital

voltmeter,communication receiver etc.

2)TNC:Threaded Neil Concelman Connectors

• In this the locking system is of threaded coupling type

instead of bayonet type.

• It is used in radio and video link and microwave.

• It is available in small size.

• It is light in weight and weather proof type.

• Its nominal impedance 50Ω.

• It is used up to frequency of 11GHz.

3)N :

• These are medium size connector

• It is used up to 11GHz

• Its nominal impedance 50Ω

• voltage rating is 1000 V rms

4)UHF:

• These are general purpose ,low cost and threaded

coupling type connector.

• It is used in low frequency upto 300MHz. So, there is no

problem of mismatch.

• Its peak voltage rating 500V

RJ-45:

• This is of eight wire type connector

• It is used in telecommunication and connecting

computer to LAN(Local Area Network) especially

with Ethernet.

RS-232:

• RS-232 means Recommended standard number

232 and RS-232C is the latest version of this type of

connector.

• RS-232 is mainly used in computer.

• RS-232 is a 25 pin D type connector and most of the

PCs, 9 pin type D type connectors are used.

HDMI Connector:

• HDMI means High Definition Multimedia Interface.

• It is used for interfacing uncompressed video data and

compressed or uncompressed digital data from HDMI

to compatible digital audio device, computer monitor,

video projector and digital TV.

• Many types of HDMI devices are available. i.e. A, C

and D type.

Fig. : Type B

Fig. : Type A

5.4 Multimeters: Analog and digital multimeter

While testing the electronic equipment, it is necessary to

measure the a.c. voltage , d.c. voltage, current and

resistance in the circuit. For this a single instrument is

used which is called multimeter .

There are two types:

1) Analog multimeter

2) Digital multimeter

1) Analog multimeter

• Permanent magnet moving coil (PMMC) type meter is used

in multimeter.

• The function can be selected by the function switch.

• D.C. voltage is given through the voltage divider which is a

chain of resistors.

• Voltage is display on the scale with the help of pointer.

• The PMMC type meter is respond to d.c. voltage only.

• Different shunts are used to measure current in different

ranges.

• To measure resistance, a constant known current is passed

through the resistance to be measured. The voltage drop

across the resistance is proportional to the resistance. This

voltage drop is measured and the reading is indicated on

the scale which shows resistance in ohms.

2) Digital multimeter

Block diagram of Digital multi meter:

• Various electrical quantities like d.c. Voltage, a.c.

Voltage, d.c. Current, a.c. Current, resistance can be

measured by digital multi meter.

1) function switch:

With the help of this switch, different functions like

d.c. voltage(DCV), a.c.voltage(ACV), current

(DCA/ACV), resistance can be selected.

2) d.c. Voltage divider:

A chain of resisters is used to measure d.c. Voltages

of different ranges. Basic range of DVM is 2V.

3) rectifier:

A output d.c.voltage is proportional to the rms value

of the a.c. Voltage. Resistance chain for the voltage

divider is the same for the voltage divider is the same for

both the d.c. And a.c. Voltage measurement.

4) current sensing resistor:

Current to be measured is passed through one of the

standard resistor voltage drop across this is measured

which is proportional to the current.

6) digital volt meter (DVM):

d.c. voltage is measured by this voltmeter. Its basic

range is of 2V.This is in form of chip.

7) display(LED,LCD):

The display is either of LCD type and LED type. The

quantity measured by the DMM is display on this.

• Accuracy is more.

• Good resolution is available.

• Reading can be taken from a distance.

• There is no personal error.

• Taking reading is easy and quick.

• Wide range is available. Automatic indication of polarity:

• It is compact.

• Output is digital.

Advantages:

CRO(Cathode ray oscilloscope )

5.5 CRO: front panel controls and application

• CRO is an electronic instrument which converts electrical

signal into visual signal.

• The heart of CRO is CRT(cathode ray tube).

• In this high velocity sharp beam of electron produced.

• This beam is passed through the vertical and horizontal

deflecting plates.

• The beam then strikes the fluorescent screen and we can see

the waveform of the applied to the CRO input.

Cathode ray oscilloscope front panel

Cathode ray oscilloscope front panel controls

1.On power control:

This is a switch which is used to switch ON &

OFF the power given to CRO.

2.Intensity control:

This is one pot with the help of which the negative

voltage applied to the control grid is changed so the

intensity of the waveform is changed.

5.X shift:

with the help of this control beam and hence the

waveform can be shifted in horizontal direction.

3.Focus control:

With the help of this control the sharpness of the

beam is adjusted.

4.Y shift:

with the help of this control beam and hence the

waveform can be shifted in vertical direction.

6.Y gain:

with this control the gain of the vertical amplifier is

changed. This control is calibrated in V/cm.

7.Time base:

With this control the frequency of the time base is

changed.

8.Sync selector:

Synchronizing signal is selected with the help of

this control. There are three position of this control.

There are INT, EXT and LINE.

9. X gain:

Gain of the horizontal amplifier can be controlled

with this controlled.

10.Y input:

Unknown voltage whose wave shape has to be seen

is given to this control.

11.Input selector:

There are three position in this. If input is a.c., the

control is set to a.c..When input is d.c., the control is set

to d.c..When control is set to ground , the input is cut-off

and input lead is connected to ground.

12.External Sync input:

When the synchronizing signal is taken from the

external source it is given here.

13.X input:

When it is required to see the effect of varying one

quantity on the other quantity, the signal of the independent

quantity is applied here.

14.Graticule:

For the measurement of the waveform vertical

and horizontal scales are inscribed on the screen. This

is called the Graticule.

15.LED indicator:

It indicates whether the power is available to the

CRO or not.

Application of CRO

(1) Measurement of electrical quantity

(2) Measurement of unknown voltage

(a) D.C.voltage

(b) A.C.voltage

(3) Measurement of electric current

(4) Measurement of unknown frequency

(a) By measuring the time period T of one wave

(b) By comparing with known frequency

(5) Measurement of phase difference-power factor

Any Question

?

Thank You